performance wise both are around same.
vram on amd is more ,however your deciding factor should be the resolution you play at.
if u are restricted to 1080p monitor, the vram wont have much effect, u could go with nvidia and get dlss/raytracing/better encoders.
if u game at 1440p, 6700xt is highly recommended.
my 6700(10gb) easily uses 6-8gb in re4 remake and last of us.